NEW YORK -- Now that it is official -- humans are almost certainly causing the most dramatic climate shift the planet has seen in thousands of years -- it is time to stop arguing and get down to the serious work of solving the problem, right?

Not so fast. If the dispute over the scientific basis of global warming was protracted, the fight over how to deal with it is bound to be even worse.

The most contentious issues: How and when should we turn the global economy away from fossil fuels? Should we dedicate resources to addressing some of global warming's effects, as well as its causes? And if so, how wise would it be to divert those resources away from prevention efforts in order to do it?

These are the big questions in the three weeks since the Intergovernmental Panel on Climate Change, a scientific body charged with assessing the evidence for and risk of global warming, declared it "very likely" that the globe's increasing temperature is a result of human activity. The panel also warned that further warming is inevitable thanks to delays and feedbacks in the climate system.

"We have reached a scientific critical mass, the question now is how do we reach a political critical mass," Republican Sen. Olympia Snowe of Maine told a World Bank-sponsored conference of legislators from 80 countries who met in Washington this month.

Snowe co-sponsors one of five U.S. Senate bills that would cap the total amount of greenhouse gases the United States emits and give polluters tradable credits entitling them to emit a fraction of the total. Polluters who emitted less than their share of greenhouse gases could sell their credits to those who did not.

The European Union, already operating under such a system, committed on Tuesday to cut its emissions limit 20 percent from 1990 levels by 2020.

A "cap-and-trade" approach is essential to preventing catastrophic global warming, said Eileen Claussen, president of the Pew Center on Global Climate Change, in testimony before the House subcommittee on energy and air quality.

Capitol Hill witnessed a cavalcade of climate change hearings this month as members of both parties took pains to voice their support for limits on greenhouse gases.

The Bush administration opposes mandatory cuts in greenhouse gas emissions, favoring a more voluntary approach. But even corporate leaders are increasingly skeptical of such a strategy; on Tuesday members of the Global Roundtable on Climate Change -- a group that includes corporations such as Alcoa, Citigroup, Ford and General Electric as well as environmental groups, universities and government representatives -- signed a statement calling for greenhouse gas targets and a pricing mechanism for emissions.

Others advocate a technical fix. Earlier this month, English billionaire Richard Branson offered US$25 million (euro19.1 million) to anyone who develops a technology that can remove at least one billion tons of carbon from the atmosphere annually for at least a decade.

"We need everybody capable of discovering an answer to put their minds to it today," Branson said.

Trying to prevent global warming is certainly worthwhile, said Roger Pielke, Jr., a professor of environmental studies at the University of Colorado.

But he said capable people are not adequately putting their minds to the challenge of adapting to climate change, which is inevitable in coming decades because of continuing emissions and because of the damage done already.

"If all we do is try to mitigate we're going to miss a big part of the challenge," Pielke said.

The world's leaders also need to address other problems that are likely to be aggravated by global warming, such as tropical diseases, drinking water supply and increasing storm vulnerability, Pielke and several colleagues argued in the scientific journal Nature.

Many global warming activists are suspicious of such recommendations. They feel that too much reliance on adaptation will lull the world into a false sense of security, decreasing the motivation to reduce greenhouse gases.

"We really have to focus on prevention," Al Gore said on Tuesday during a question-and-answer session at Columbia University in New York City.

He warned that if we fail to avert the worst of global warming, the dire environmental consequences will overwhelm any adaptive measures.

Rich countries have the resources to adapt to some of global warming's effects, and some of them already are. Officials from the Netherlands said this month they were considering adding to their low-lying nation's flood defenses by building islands in the North Sea that would buffer the mainland against storm surges.

But that is not a realistic option for countries like Vietnam and Egypt, both of which would see more than 10 percent of their populations displaced if sea level were to rise by 3 feet (91 centimeters), according to an analysis by the World Bank.

The Intergovernmental Panel on Climate Change does not foresee such extreme sea-level rise for at least a century. But there is an asterisk attached to that projection -- not enough is known about how the massive ice sheets covering Greenland and Antarctica will react as temperatures rise. Some scientists think the effects will be relatively minor, but others point to past warm periods when the amount of ice at the poles was much smaller and sea level much higher. They also point to troubling signs of instability, especially in Greenland, where satellite measurements show accelerated melting of the ice cap in recent summers.

"I think they should warn people more strongly about that danger, because I think it's the greatest danger that humanity faces in the global warming problem," NASA climate scientist James Hansen in an interview with the public radio program "Living on Earth."

Hansen was one of seven prominent scientists who pointed out in the journal Science this month that global sea level has actually risen faster than the Intergovernmental Panel on Climate Change projected in its first report 17 years ago. The panel's 1990 temperature prediction was also on the low side.

It will take scientists decades to fully understand how carbon dioxide and other human-generated greenhouse gases are affecting Earth's climate. And it will take Herculean political efforts to make a significant dent in the ever-growing release of those gases into the atmosphere by smokestacks, tailpipes and burning forests.

But in the meantime, advocates of adaptation say, we should not forget that it cannot hurt to prepare for the effects of global warming, because they are going to come no matter what we do.